Presently used magnetic recording materials include magnetic oxide powder and ferromagnetic alloy powder, such as .gamma.-Fe.sub.2 O.sub.3, Co-doped .gamma.-Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4, Co-doped Fe.sub.3 O.sub.4, a Berthollide compound of .gamma.-Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4, and CrO.sub.2. These powders are dispersed in an organic binder, e.g., a vinyl chloride/vinyl acetate copolymer, styrene/butadiene copolymer, an epoxy resin, or a polyurethane resin, and coated on a non-magnetic support. In recent years there has been increasing demand for high density recording. Accordingly, there has been increased demand for so-called thin metal film type magnetic recording materials with a thin ferromagnetic metal film as a magnetic recording layer. These thin ferromagnetic metal films are produced by vapor deposition methods such as vacuum deposition, sputterning, or ion plating, or plating methods such as electroplating or non-electroplating. Thus, extensive studies have been made on such thin metal film type magnetic recording materials in order to put them to practical use.
Since conventional coating type magnetic recording materials mainly employ metal oxides of low saturation magnetization as magnetic substances, the reduction in thickness of the magnetic recording material (this reduction in thickness being necessary for high density recording) lowers the signal output. For this reason, coating type magnetic recording materials suffer from limitations with respect to high density recording. On the other hand, the thin metal film type recording materials are desirable because ferromagnetic metals of greater saturation magnetization than the metal oxides can be formed into a very thin film without interposing therebetween a non-magnetic substance, such as a binder.
These thin metal film type magnetic recording materials, however, suffer from serious problems as described hereinafter. That is, since the magnetic recording materials are brought into a relative movement while contacting with magnetic heads and guide poles during the processes of recording, reproducing, and erasing magnetic signals, they are worn out or broken by contact with the magnetic heads and guide poles. For example, when they are placed in a sliding contact condition with the magnetic heads and guide poles, the magnetic recording layer may be easily scraped away, since the magnetic recording layer does not contain material such as binder.
In order to overcome the above problem, an attempt has been made to coat the magnetic recording layer with, for example, a polymer film having a thickness of about 0.2 .mu.m. This method, however, is not desirable in that the overcoating causes a spacing loss which causes output drop in high density recording.
It is also known that the coating of a lubricant on the surface of the magnetic recording layer in a thin layer form reduces the coefficient of friction between the thin metal film and the magnetic head or guide pole, and improves the running properties, whereby the resulting magnetic recording material is scratched only with difficulty. In this case, however, the effects obtained by coating such lubricants do not last for a long period of time, and, when the magnetic recording material is used repeatedly, the coefficient of friction increases abruptly, resulting in a break-down of the magnetic recording layer.
Another method of overcoming the above problem is to form a lubricant protective layer of, for example, metal or metal oxide on the surface of the magnetic recording material, as disclosed in Japanese Patent Application (OPI) Nos. 39708/78 and 40505/78 (the term "OPI" as used herein means a "published unexamined Japanese patent application". However, the effects obtained by forming the lubricant protective layer also do not last for a long period of time, and, when the magnetic recording material is used repeatedly, the coefficient of friction increaes abruptly, resulting in a break-down of the magnetic recording layer.